What I'm thinking about the Random and Date folders in Commander (and Jaesen will correct me if I'm wrong

) is that they can only be used to insert/overwrite files in the game folder when Commander is used to launch SH3. I don't think they can be used to make Commander itself operate differently, or switch back and forth between two or more versions of one of its own .cfg files depending on the in-game date for whatever career you're updating/playing at the moment.
My idea was to create two mods, one for before Dec 10 1941 and another for that date and after. The first one would have the edited down version of whatever the current Shipnames.cfg file is, the other would have the full lists of ship names for use after the US enters the war. Then I would enable/disable them as needed depending on what date I was playing in-game.
But that wouldn't work as smoothly for someone who is playing more than one career using the same installation of Commander, they'd have to remember to switch back and forth more often depending on which career they were going to choose and what the current in-game date was for that particular kaleun.
If there were a way to make that "automatic" within Commander itself that would be very handy but if there is it's still a mystery to me.